const Gtk = imports.gi.Gtk;

Gtk.init (null, 0);
let win = new Gtk.Window ({type : Gtk.WindowType.TOPLEVEL});
let label = new Gtk.Label ({label : "Hello World"});
win.title = "Hello World!";
win.connect ("destroy", function () {Gtk.main_quit()});
win.add (label);

label.show ();
win.show ();

Gtk.main();